1. Field of the Invention
The present invention relates to an air conditioning system including an indoor heat exchanger as part of a refrigeration circuit. More specifically, the present invention concerns a method for controlling an indoor fan located to circulate air from an enclosure through the indoor heat exchanger of the refrigeration circuit and back to the enclosure. A fan control is provided for allowing an operator to select continuous fan operation in which the fan is operated continuously or automatic operation in which the fan is operated together with a compressor of the refrigeration circuit.
2. Description of the Prior Art
Air conditioning systems, including straight cooling systems and heat pumps, typically have a thermostat located in the space to be conditioned to determine whether the enclosure temperature is too high or too low. Upon sensing a temperature variation from the desired range a thermal sensing element typically closes indicative that air conditioning, either heating or cooling, is necessary. Additionally, some thermostats include a fan control switch therewith such that the fan may be operated either independently from the refrigeration circuit or in conjunction with the refrigeration circuit.
Thermostats incorporating a switch between automatic and continuous on control are known in the art. A brief description of one may be found in U.S. Pat. No. 4,178,988 issued to the assignee hereof and disclosing therein a thermostat for the control of a combination furnace and heat pump.
In the present application a microprocessor control is utilized in conjunction with this thermostat to control the operation of the air conditioning system including the operation of the indoor fan as well as the compressor of the refrigeration circuit. A central processing unit of the microprocessor control receives signals from the thermostat indicating certain functions. A first signal is received when it is desired to operate the compressor either in the cooling or heating modes of operation. The second signal is received when it is desired to operate the fan. When a heating or cooling cycle is completed the microprocessor control will at that point detect whether or not the second signal is still being generated and based thereon determine whether or not to operate the fan continuously.
In most refrigeration systems there are various overloads and safeties provided to prevent operation of the compressor under certain operating conditions. Safety conditions such as high pressure or low pressure in the refrigeration circuit as well as electrical conditions such as ground fault, welded contacts or timing devices such as an interrupt device to prevent short cycling of the compressor are utilized to prevent the compressor from operating notwithstanding a first signal being generated through the thermostat calling for compressor operation. In order to effectively control the operation of the compressor and the indoor fan it has been found advantageous to determine firstly whether or not a signal is being generated to indicate a demand for compressor operation. Thereafter, it may be determined whether or not the compressor is actually operating or if it is tripped off on a safety. If the compressor is tripped off on a safety then, absent other considerations, the indoor fan will not operate notwithstanding that it may have been manually set in the continuous position. The herein invention provides a method of assuring that notwithstanding the signals sensed if there is demand for compressor operation and the compressor is not operating that there will be available a method for operating the fan continuously.
The control as described acts to remember the state of the second output by setting a flag. At a later point it can be determined whether or not this flag is set and based upon the indication of the flag, the fan may be operated continuously notwithstanding the compressor not operating.